BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive cyst expansion, fibrosis and inflammation, leading to kidney failure. Myofibroblasts (MFs) often accumulate around cysts and promote fibrosis and cyst growth, but the cellular mechanisms enabling their pro-cystogenic activity remain unclear. Here we examined the role of autophagy within MFs, on their paracrine stimulation of cyst expansion in ADPKD.
METHODS: Autophagy was assessed in human ADPKD nephrectomy tissue, primary human ADPKD renal myofibroblasts (ADPKD-MFs) and male RC/RC mouse model of ADPKD using immunostaining, LC3/p62 analyses, and transmission electron microscopy. Autophagy in MFs was inhibited pharmacologically in ADPKD-MFs, or by conditional Atg5 deletion in PDGFRβ-expressing renal stromal cells in RC/RC (RC/RC;Atg5KO) and wild type (WT;Atg5KO) mice.
RESULTS: In human and mouse ADPKD kidneys, we detected LC3 puncta and autophagic organelles within αSMA-expressing MFs. Inhibition of autophagy in ADPKD-MFs blocked their paracrine stimulation of cyst epithelial cell proliferation. RC/RC;Atg5KO mice showed significantly reduced cystic growth, fibrosis, MF abundance, and improved kidney function. WT;Atg5KO mice showed no abnormalities in kidney structure or function. Targeted metabolomics performed on ADPKD cyst epithelial-cell conditioned media (ADPKD-ECs CM) revealed moderate increase in lactate levels compared to normal human kidney epithelial-cell conditioned media. Furthermore, lactate treatment stabilized hypoxia-inducible factor-1α (HIF1α) in myofibroblasts, while pharmacological inhibition of HIF1α reduced the expression of autophagy-related genes and impaired autophagic flux. in vitro
CONCLUSION: These findings reveal that autophagy in MFs is a previously unrecognized driver of cyst expansion and fibrosis in ADPKD. Lactate-mediated HIF1α stabilization in MFs promotes autophagy that is required for their paracrine stimulation of cyst epithelial growth. Targeting MF-specific autophagy or its upstream regulators may represent a therapeutic strategy to limit cyst growth and fibrosis in ADPKD.
